The luminosity-to-mass ratios of clumps A–D were derived to be about \(0.4\pm 0.1\) , \(0.4\pm 0.1\) , \(0.5\pm 0.1\) , and \(1.0\pm 0.4\)  L\(_{}\) /M\(_{}\) , respectively (the uncertainties were propagated from both quantities, and a mean value of the \(\pm \)  uncertainties in \(L\)  was used in the calculation). Because the \(L/M\)  ratio is expected to increase as the clump evolves, it can be used as an indicator of the clump evolutionary stage (e.g. [1]}; [2]}; [3]}). We note that a similar evolutionary indicator (bolometric luminosity-to-envelope mass ratio, \(L_{\rm bol}/M_{\rm env}\) ) is also used for low-mass – class 0 and class I – embedded protostars (e.g. [4]} for a review). On the basis of this, clumps A and B appear to be the least evolved sources in the filament. Clump B in the centre of the filament is also associated with only a weak 70 \(\mu \) m source. Clumps C and D appear to be somewhat more evolved sources owing to their slightly higher \(L/M\)  ratio (the differences in \(L/M\)  are not significant within the uncertainties). Clumps C and D are both associated with 24 \(\mu \) m sources, which also suggests that the clumps are hosting more evolved embedded YSOs.
